Coriolis flowmeter with zero checking feature

ABSTRACT

Descriptions are provided for implementing flowmeter zero checking techniques. In operating a flowmeter, it may be the case that, even if previously calibrated, the flowmeter will produce erroneous measurements, will indicate a non-zero flow during a period of zero flow. Therefore, zero checking features are provided that allow for fast and accurate determinations of the zero-flow values, for use in adjusting later measurements. The zero-checking features include a button attached to an exterior of a flowmeter, so that it is easily accessible to an operator of the flowmeter. The button, in conjunction with an internal zero checking system, allows for a display of a zero value in response to a request from the operator of the flowmeter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/016,574, filed Jan. 18, 2008, titled CORIOLIS FLOWMETER WITH ZEROCHECKING FEATURE, now U.S. Pat. No. 7,979,230, which is a continuationof U.S. patent application Ser. No. 11/157,157 filed Jun. 21, 2005, nowU.S. Pat. No. 7,337,084, titled SWITCH-ACTIVATED ZERO CHECKING FEATUREFOR A CORIOLIS FLOWMETER. The prior applications are hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

This description relates to flowmeters.

BACKGROUND

Flowmeters provide information about materials being transferred througha conduit. For example, mass flowmeters provide a measurement of themass of material being transferred through a conduit. Similarly,densitometers provide a measurement of the density of material flowingthrough a conduit. Mass flowmeters also may provide a measurement of thedensity of the material.

For example, Coriolis-type mass flowmeters are based on the Corioliseffect, in which material flowing through a conduit is affected by aCoriolis force and therefore experiences an acceleration. ManyCoriolis-type mass flowmeters induce a Coriolis force by sinusoidallyoscillating a conduit about a pivot axis orthogonal to the length of theconduit. In such mass flowmeters, the Coriolis reaction forceexperienced by the traveling fluid mass is transferred to the conduititself and is manifested as a deflection or offset of the conduit in thedirection of the Coriolis force vector in the plane of rotation.

SUMMARY

According to one general aspect, a method includes detecting a manualoperation of an input device that is connected to a controller of aflowmeter, the controller being operable to output measurements of amass flow rate of a fluid within a vibratable flowtube associated withthe flowmeter. The method also includes determining that the manualoperation of the input device corresponds to a request for checking azero flow rate calibration value that is present during a time of zeroflow of the fluid within the flowtube, performing an averaging operationon a series of the measurements over a pre-determined time period andduring the time of zero flow, to obtain an averaged zero flowcalibration value, and outputting the zero flow calibration value, inresponse to the request.

Implementations may include one or more of the following features. Forexample, detecting the manual operation of the input device may includedetecting operation of a switch that is connected to a casing of thecontroller. Operation of the switch may be detected through a contactinput connected to the switch and to the controller, where the switch isaccessible externally to the casing, and without requiring direct accessto the controller within the casing. Determining that the manualoperation of the input device corresponds to the request for checkingthe zero flow rate calibration value may include determining that switchis activated for greater than a second predetermined time.

Outputting the zero flow calibration value may include displaying thezero flow calibration value on a display associated with the controller.Additionally or alternatively, outputting the zero flow calibrationvalue may include outputting a standard deviation of the zero flowcalibration value.

Detecting the manual operation of the input device that is connected tothe controller of the flowmeter may include detecting the manualoperation of the input device that is connected to the controller of aCoriolis flowmeter.

In another example, the method may further include modifying subsequentmeasurements of the controller during a subsequent time of non-zeroflow, based on the zero flow calibration value, to obtain adjustedmeasurement outputs, connecting a proving meter to pulse outputterminals connected to the controller, and testing an accuracy of theflowmeter, based on outputs of the proving meter and the adjustedmeasurement outputs of the flowmeter.

The method may include performing the averaging operation multiple timesover each of a number of periods of zero flow, detecting a trend ofchange in resulting zero flow calibration values, and outputting analarm signal notifying impaired performance of the flowmeter, based onthe trend.

The method may include detecting that a magnitude of the zero flowcalibration value exceeds a pre-determined value, and outputting analarm signal notifying impaired performance of the flowmeter, based onthe detection of the magnitude exceeding.

According to another general aspect, a system includes a controller thatis operable to output drive signal information for driving a vibratableflowtube, and receive sensor information reflecting a vibration of theflowtube. A measurement system is associated with the controller that isoperable to generate measurements of a mass flow rate of a fluid withinthe flowtube, based on the sensor information. A manually-activatedinput device is connected to an exterior of the controller, foractivation by an operator of the controller. A zero checking system isassociated with the controller and is in communication with the inputdevice and the measurement system. The zero checking system is operableto detect the activation of the input device and perform an averagingoperation on a series of measurements from the measurement system over apre-determined time period and during a time of zero flow of the fluidwithin the flowtube, to obtain an averaged zero flow calibration value,in response to the activation. The system also may include a display fordisplaying the averaged zero flow calibration value.

Implementations may include one or more of the following features. Forexample, the system may include a casing containing the controller,wherein the input device is located externally to the casing and isconnected to the controller through a contact input of the casing. Theinput device may be included within a connection module that is attachedto the contact input. The input device may be a switch, and theactivation of the input device may include pressing of the switch by theoperator.

The zero checking system may be further operable to distinguish betweena first type of activation of the input device, for which nodetermination of the zero flow calibration value desired, and a secondtype of activation of the input device, for which determination of thezero flow calibration value is desired. The controller may be a Coriolisflowmeter controller.

The zero checking system may be operable to de-activate a low-flowcutoff system for masking the measurements of the mass flow rate below adefined value, in response to the activation of the manually-activatedinput device.

According to another general aspect, an apparatus comprising a storagemedium having instructions stored thereon is provided. The instructionsmay include a first code segment for controlling and analyzing avibration of a flowtube, so as to determine measurements of a mass flowrate of a fluid within the flowtube, a second code segment for receivingan activation signal corresponding to an activation of a switch, and foranalyzing the activation signal to determine that a zero-checkingoperation is desired, a third code segment for performing thezero-checking operation by analyzing the measurements during a time ofan actual zero flow rate of the fluid, to determine a zero-flowcalibration value, and a fourth code segment for outputting thezero-flow calibration value.

Implementations may include one or more of the following features. Forexample, the third code segment may include a fifth code segment foraveraging the measurements over a pre-determined time period within thetime of actual zero flow rate of the fluid, and for determining astandard deviation associated with the averaging of the measurements.

The fourth code segment may output the zero-flow calibration value to adisplay screen for display. The second code segment may include a fifthcode segment for receiving the activation signal from a host computer incommunication with the apparatus.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is an illustration of a Coriolis flowmeter using a bentflowtube.

FIG. 1B is an illustration of a Coriolis flowmeter using a straightflowtube.

FIG. 2 is a block diagram of a Coriolis flowmeter.

FIG. 2A is a block diagram of another embodiment of a Coriolisflowmeter.

FIG. 3 is a block diagram of an implementation of the flowmeter of FIG.2.

FIG. 4 is a flowchart illustrating a zero-checking operation.

FIG. 5 is a block diagram of an application of the flowmeters of FIGS. 2and 3.

DETAILED DESCRIPTION

Types of flowmeters include digital flowmeters. For example, U.S. Pat.No. 6,311,136, which is hereby incorporated by reference, discloses theuse of a digital flowmeter and related technology including signalprocessing and measurement techniques. Such digital flowmeters may bevery precise in their measurements, with little or negligible noise, andmay be capable of enabling a wide range of positive and negative gainsat the driver circuitry for driving the conduit. Such digital flowmetersare thus advantageous in a variety of settings. For example,commonly-assigned U.S. Pat. No. 6,505,519, which is incorporated byreference, discloses the use of a wide gain range, and/or the use ofnegative gain, to prevent stalling and to more accurately exercisecontrol of the flowtube, even during difficult conditions such astwo-phase flow.

Although digital flowmeters are specifically discussed below withrespect to FIGS. 1 and 2, it should be understood that analog flowmetersalso exist. Although such analog flowmeters may be prone to typicalshortcomings of analog circuitry, e.g., low precision and high noisemeasurements relative to digital flowmeters, they also may be compatiblewith the various techniques and implementations discussed herein. Thus,in the following discussion, the term “flowmeter” or “meter” is used torefer to any type of device and/or system in which a Coriolis flowmetersystem uses various control systems and related elements to measure amass flow, density, and/or other parameters of a material(s) movingthrough a flowtube or other conduit.

FIG. 1A is an illustration of a digital flowmeter using a bent flowtube102. Specifically, the bent flowtube 102 may be used to measure one ormore physical characteristics of, for example, a (traveling) fluid, asreferred to above. In FIG. 1A, a digital transmitter 104 exchangessensor and drive signals with the bent flowtube 102, so as to both sensean oscillation of the bent flowtube 102, and to drive the oscillation ofthe bent flowtube 102 accordingly. By quickly and accurately determiningthe sensor and drive signals, the digital transmitter 104, as referredto above, provides for fast and accurate operation of the bent flowtube102. Examples of the digital transmitter 104 being used with a bentflowtube are provided in, for example, commonly-assigned U.S. Pat. No.6,311,136.

FIG. 1B is an illustration of a digital flowmeter using a straightflowtube 106. More specifically, in FIG. 1B, the straight flowtube 106interacts with the digital transmitter 104. Such a straight flowtubeoperates similarly to the bent flowtube 102 on a conceptual level, andhas various advantages/disadvantages relative to the bent flowtube 102.For example, the straight flowtube 106 may be easier to (completely)fill and empty than the bent flowtube 102, simply due to the geometry ofits construction. In operation, the bent flowtube 102 may operate at afrequency of, for example, 50-110 Hz, while the straight flowtube 106may operate at a frequency of, for example, 300-1,000 Hz.

Referring to FIG. 2, a digital mass flowmeter 200 includes the digitaltransmitter 104, one or more motion sensors 205, one or more drivers210, a flowtube 215 (which also may be referred to as a conduit, andwhich may represent either the bent flowtube 102, the straight flowtube106, or some other type of flowtube), and a temperature sensor. Thedigital transmitter 104 may be implemented using one or more of, forexample, a processor, a Digital Signal Processor (DSP), afield-programmable gate array (FPGA), an ASIC, other programmable logicor gate arrays, or programmable logic with a processor core.

The digital transmitter 104 generates a measurement of, for example,density and/or mass flow of a material flowing through the flowtube 215,based at least on signals received from the motion sensors 205. Thedigital transmitter 104 also controls the drivers 210 to induce motionin the flowtube 215. This motion is sensed by the motion sensors 205.

Density measurements of the material flowing through the flowtube arerelated to, for example, the frequency of the motion of the flowtube 215that is induced in the flowtube 215 by a driving force supplied by thedrivers 210, and/or to the temperature of the flowtube 215. Similarly,mass flow through the flowtube 215 is related to the phase and frequencyof the motion of the flowtube 215, as well as to the temperature of theflowtube 215.

The temperature in the flowtube 215, which may be measured using atemperature sensor, affects certain properties of the flowtube, such asits stiffness and dimensions. The digital transmitter 104 may compensatefor these temperature effects. Other sensors may be included, such as,for example, a gas void fraction sensor that is operable to determinewhat percentage of a material in the flowtube 215, if any, is composedof a gas, or a pressure sensor that is operable to sense a pressure of amaterial flowing through the flowtube 215.

In performing measurements of mass flow (and/or density), calibration ofthe flowmeter may be required in order to maintain system performance,particularly over long periods of time and/or extensive operation of theflowmeter. One calibration technique is known as “zeroing” or “a zerocalibration.” In a zeroing process, a flow of material through theflowtube 215 is stopped (for example, upstream and downstream valves maybe closed) during a time when the flowtube 215 is filled with thematerial. As a result, there is a zero flow of the material, whichshould, ideally, lead to a corresponding reading of zero flow output bythe flowmeter.

For various reasons, however, it may be the case that the flowmeteroutputs a non-zero (i.e., erroneous) flowrate during a time of zeroflow. In these cases, the (erroneous) non-zero flowrate at zero flow maybe used as a calibration factor; that is, for example, it may besubtracted from (or added to) a measured flow, so as to obtain anaccurate, i.e., zero-corrected, reading of the flow during futurereadings.

For example, when more than one of the sensor(s) 205 are used, there maybe some phase difference in signals that are output from the sensors 205that is inherent to the structure or operation of the sensors 205relative to one another. Even if attempts are made to “balance” thesensors 205 with respect to one another, it may be the case that, sincethe mass flow rate of the fluid in the flowtube 215 may be determined atleast partially based on such phase differences, the transmitter 104 maydetect a non-zero mass flow rate of the fluid in the flowtube 215 duringzero flow. Similarly, non-zero mass flow rates may be detected duringzero flow, due to, for example, external vibrations or disturbances ofthe transmitter 104, or due to a change in a type of fluid within theflowtube 215, or due to a changed configuration of the flowtube 215and/or surrounding piping, or for other reasons.

Moreover, in some cases, such non-zero mass flow rates detected duringzero flow may be extremely transient, and may be prone to exhibit a widerange of quickly-changing values, during a relatively short period oftime. In many applications, such values may be effectively discarded orignored, if they are very small relative to an amount of fluid beingprocessed, or if a high degree of accuracy is not required.

In other applications, however, non-zero mass flow rates detected duringzero flow may be very important to determining mass flow rates of fluidthrough the flow tube 215. For example, in gas and oil applications, inwhich an operator uses the flowmeter 200 to determine an amount of, forexample, oil that is being transferred (measured in barrels per day, orbpd), then a number of barrels of oil may correlate with a large dollarvalue, so that high levels of accuracy and repeatability are desirable.

In FIG. 2, then, the digital transmitter 104 includes various elementsdesigned to quickly, accurately, and easily determine a current zerovalue (i.e., a non-zero mass flow rate detected during zero flow). Suchzero checking capabilities and features further provide for zerodetection in a manner that does not require access to internal workingsof the transmitter 104, and that allows for a high repeatability ofmeasurements from the flow meter 200.

That is, FIG. 2 includes a calibration system 220 that refers to asystem for implementing a pre-set zero value, in conjunction with ameasurement system 225. The measurement system 225 refers generically tothe systems of the transmitter 104 that measure, for example, a densityor mass flow rate of the fluid within the flowtube 215, based on signalsfrom the sensors 205, as described above.

As also described, the resulting mass flow rate values may includenon-zero mass flow rates detected during zero flow, which may be, forexample, factory-measured to determine an appropriate calibration value.This calibration value may then be used to correct mass flow rate valuesthat are determined/output by the measurement system 225, for display ona display 230.

In other words, the ideal or theoretical situation is that themeasurement system 225 outputs a zero value at zero flow, and thecalibration system 220 is not needed. In practice, this is often not thecase, and so the calibration system 220 is configured with the intent ofaltering the output of the measurement system 225 by a measuredzero-flow rate value, so that the output of the transmitter 104 itselfis zero at zero flow. Even with the calibration system 220, however, asdescribed, the resulting mass flow rate that is output, particularlyover time and over a variety of circumstances, may be non-zero at zeroflow. That is, in many cases, the practical effect of the calibrationsystem 220 is to reduce, but not entirely to eliminate, a non-zeroreading at zero flow.

In some circumstances, the calibration system 220 may be re-configuredwith additional or corrected zero-flow calibration values. However, sucha re-configuration may require a level of access to the operation of thetransmitter 104 that is either not available or not desired. Forexample, once the digital transmitter 104 is manufactured and sold to acustomer, then that customer may not have the time, the tools, theexpertise, or the desire to re-configure the calibration system 220.

In particular, when the flow meter 200 is used in field operations, suchas the transfer of large volumes of oil, as mentioned above, it may beimpractical to expect or require available technicians to have theresources to re-configure the calibration system 220. For example, sucha re-configuration may require access to the transmitter 104 within apackaging or casing 235, which may be difficult or inconvenient.Further, opening the casing 235 may expose certain inputs/outputs orvoltages of the transmitter 104, the mis-handling of which could lead toimpairment or failure of the transmitter 104.

In such cases, a “low-flow cutoff” may be established, which is anartificial flow rate value determined by an operator, below which thetransmitter automatically outputs a value of zero for the determinedflow rate. In other words, such a cutoff masks the appearance ofnon-zero mass flow rates during zero flow, without really accounting forthe effect(s) thereof. Such a low-flow cutoff may make an operation ofthe flow meter 200 appear to be more accurate than the flow meter 200actually is, and does not do away with a need for field operators toaccess and determine a current zero flow value for the flow meter 200.

Thus, in FIG. 2, a secondary casing and/or lid 240 is provided, whichexposes certain functionality of the flow meter 200, as described inmore detail below, without exposing an interior of the casing 235. Inparticular, the lid 240 may be lifted to expose a switch or button 245,which is functionally connected to the digital transmitter 104 by way ofa contact input 250 that is associated with the transmitter 104 and withthe casing 235.

The button 245 may be used, as described in various examples below, tocheck a current value of a non-zero mass flow rate detected at zero flow(referred to hereafter as a “zero value,” a “zero flow value,” or thelike), in an easy, accessible, reliable, and accurate way. For example,once a zero flow rate is established through the flow tube 215, by, forexample, closing upstream and downstream valves associated with theflow, then a simple pressing and/or holding of the button 245 outputs acurrent zero flow reading, averaged over some pre-determined time, andusing the display 230. This current zero flow reading may then besubtracted from, or added to, future readings of the flow meter 200, inorder to obtain a more accurate measurement therefrom.

Although instantaneous zero flow values may be obtained simply byreading the display 230, such instantaneous values may be inaccurate, ormay be largely or completely useless in practical situations. Forexample, if an operator of the flow meter 200 simply establishes a zeroflow condition and reads the display 230, the display will, in manycircumstances, display transient, changing, and widely-varying zero flowvalues. In this case, the operator may be forced to use the worst,highest, or most extreme zero flow value, in order to ensure a baselinelevel for readings of the flow meter 200, and in order to ensure thatflow volumes calculated by the flow meter 200 are, at the least, notunder-reported, even if they are inaccurate.

Thus, generally speaking, pressing the button 245 activates a zerochecker 255 associated with the transmitter 104, which calculates acurrent, e.g., an average, reading of the zero value, based on outputsof the measurement system. Such a reading will generally be moreaccurate and more reliable than a sight-reading performed by theoperator, and will thus lead to improved measurements being used by theoperator.

In one implementation, the zero checker 255 is operable, upon activationof the button 245, automatically to disable or remove any low-flowcutoff value that may presently be instituted with respect to the flowmeter 200. For example, as referenced above, the digital transmitter maybe configured to display a zero value on the display 230, anytime that aflow rate output of the flow meter 200 is less than some pre-determinedvalue. Such a low-flow cutoff value may be useful for the sake ofappearance or convenience, but, in fact, may mask non-trivial errors inthe read-out of the flow meter 200. Thus, in this implementation,activation of the button 245 and, thereby, the zero-checker 255,disables any existing low-flow cutoff value that may be in effect, sothat an operator may observe any transient zero-flow read-outs thatoccur, as well as the final, averaged zero value that is provided on thedisplay 230.

Although the button 245 is illustrated in FIG. 2 as a single button, itshould be understood that multiple buttons may be used, as illustratedin FIG. 2A, e.g., a first button 245 to close the flowtube such that thefluid contained in the flowtube is stationary and initiate a zero flowreading and a second button 245′ to end a zero flow reading and to openthe flowtube such that the fluid contained in the flow tube flows. Also,other implementations may use other input techniques than a button, andmay use, for example, a switch, a turn-knob or dial, a toggle, a lever,or any other manually operated input device.

Also, although the display 230 is illustrated in FIG. 2 as being underthe lid 240, it should be understood that the display 230 may beimplemented separately from the lid 240, so that the display 230 remainsvisible at all times during use of the flow meter 200. Alternatively,there may be an opening or window in the lid 240 that allows viewing ofthe display 230. As another alternative, the button 245 and the pulseoutputs 260 may be implemented together in a single module, e.g., ajunction box as described below, and may be jointly connected to thecontact input 250 by way of the module.

Additionally, or alternatively, in FIG. 2, a host computer 265 may beused to send digital commands to the transmitter 104 by way of anintegrated communication interface 270, in order to initiate a zero flowreading and to end a zero flow reading, and to return an average zeroreading value to a digital register to be read by the host computer 265,for display in association with the host computer 265 or otherwise.

FIG. 2 also shows that a handheld device 275 may communicate with thetransmitter 104 through communication interface 270. The handheld device275 may include, among other types of suitable computing devices, a PDAstyle computing device or a personal computing device such as a laptopcomputer. The handheld device 275 may communicate with the transmitter104 via the communication interface 270 through a communication link280, which may include a wireless link (e.g. via a variety of infraredsignals/protocols or radio frequency signals/protocols such as WiMax,WiFi, Bluetooth®, or other suitable wireless communicationsignals/protocols) or a wired connection. Communication between thehandheld device 275 and the transmitter 104 may be through a directcommunication link established only between the handheld device 275 andthe transmitter 104, or may be established through a larger areacommunication infrastructure such as a process control network (e.g.represented by communication link 280) to which the handheld device 275,transmitter 104, as well as other process controllers or control systemsare connected, including for example the host computer 265.

The handheld device 275 may include a user interface that emulates thedisplay and user interface of the transmitter 104 so that informationpresented on the display 230 associated with the transmitter 104 issimultaneously presented in the user interface of the handheld device275. The user interface of the handheld device 275 also may include avirtual button or an actual physical button or key that when selected ordepressed will simultaneously activate the contact input 250 by way ofthe communication links described herein for activating the zero checker255 and initiating the zero-checking operations.

FIG. 3 is a block diagram of a flowmeter 300 that represents animplementation of the flowmeter of FIG. 2. In FIG. 3, the flowmeter 300includes a junction box (j-box) 302, i.e., a box or module that is usedto provide electrical/wiring connection, is used to house the button 245and the pulse outputs 260. The j-box 302 generally corresponds, then, tothe supplemental casing/lid 240 of FIG. 2, although the j-box 302 is notexplicitly illustrated with a lid or cover in FIG. 3.

In FIG. 3, the button 245 may include a momentary closure,spring-return, push-button switch that is connected to the contact input(switch) 250. Further, the pulse outputs 260 may be wired/jumpered froma 24V DC supply of the transmitter 104, so that the pulse outputs 260are self-powered.

FIG. 4 is a flowchart 400 illustrating a zero-checking operation foroperating the flow meters 200 and 300 of FIGS. 2 and 3. In FIG. 4, it isassumed that a zero flow condition has been established within theflowtube 215, e.g., that upstream and downstream valves have beenclosed.

Then, the process begins with a normal display (402) on the display 230,e.g., with transient and widely-varying readings of non-zero flow rates,despite the fact that zero flow has been established. As describedabove, an operator of the flow meter may have to lift a lid or otherwiseexpose the display 230 for viewing.

By pressing the button 245 for some pre-determined time, e.g., twoseconds (404), the operator may activate the zero checker 255, so thatthe display 230 reads “check zero?,” as shown in FIG. 3 (406). If theoperator does not wish to check the zero flow value, then the processmay return to providing a normal display. In this case, the operator mayindicate “no” as an answer to the “check zero?” query by pressing thebutton 245 for less than a second, or, more generally, for less thansome pre-determined amount of time.

If the operator does wish to check the zero flow value, then theoperator may indicate such a “yes” answer to the “check zero?” query bypressing the button 245 for two seconds or more, or, again moregenerally, for greater than some pre-determined amount of time. Inresponse to such an affirmative request, the zero checker 255 maypresent a “start checking?” query on the display 230 (408).

Here again, if the operator does not wish to start checking the zeroflow value after all, then the process may return to providing a normaldisplay. In this case, again, the operator may indicate “no” as ananswer by pressing the button 245 for less than a second.

If the operator, however, indicates “yes” to the “start checking?”query, by pressing the button 245 for more than two seconds, then thezero checker 255 may automatically begin to input and averagemeasurements from the measurement system 225, and may continue doing sofor a pre-determined amount of time “t” seconds, such as, for example,thirty seconds.

As explained above, the non-zero mass flow rate values detected by themeasurement system 225 during this time of zero flow may generally betransient and widely-varying, over the selected time period “t.” If theoperator were forced to determine a zero flow value based on suchoutputs, then the result would likely be either a “worst case scenario,”which may result in unacceptably inaccurate readings, or would be aninaccurate estimate that is guessed by the operator, which may resultnot only in inaccurate measurements, but measurements which under-reportan amount of fluid processed by the flow meter 200/300.

The zero-checker 255, however, determines an averaged zero flow value(410), and then outputs the averaged zero flow value and associatedstandard deviation value (412), which provides both increased accuracyand information as to an amount of variability of the zero flow valueand associated measurements. In this way, the operator may quickly andeasily obtain an improved zero flow value, which may be shown on thedisplay 230 for some pre-determined amount of time, such as, forexample, thirty seconds (414).

FIG. 5 is a block diagram of an application of the flowmeters of FIGS. 2and 3. Specifically, FIG. 5 illustrates a proving application that iscommon to, for example, the oil and gas industry, in which, again forexample, barrels of oil are measured for transfer between two entities.

In a further example of such an application, a first entity is producingor possessing oil, which is being measured for transfer using theCoriolis flowmeter 200/300 of FIGS. 2 and 3. In such a case, the second,receiving, entity may wish to verify or prove an accuracy of theflowmeter 200/300, in order to ensure accuracy in determinations of anamount of oil being transferred.

As a result, a proving meter 502 is utilized in series with theflowmeter 200/300, and connected with piping or tubing 504. Generallyspeaking, the proving meter 502 allows for a known volume of fluid (oil)to pass therethrough, so that this known volume may be compared to avolume measured by the flowmeter 200/300. For example, a number ofpulses output by the flowmeter 200/300 may be counted, for comparison toan output of the proving meter 502.

That is, depending on the type of meter used as the proving meter 502,the proving meter 502 may be connected directly to the pulse outputs 260(not explicitly shown in FIG. 5), and pulses output by the flowmeter200/300, representing a mass flow rate detected by the flowmeter200/300, may be counted to see if they match an expected number thatwould correlate with the known volume of the proving meter 502.

One type of the proving meter 502 is known as a piston prover, or acompact prover, which operates by moving an internal piston to initiatea pulse counting process. A movement range of the piston corresponds toa known fluid volume, so that completion of the movement range signals astop of the pulse counting operation.

By repeating this process multiple times, an accuracy and repeatabilityof the flowmeter 200/300 may be determined. From these values, a “meterfactor” may be obtained, which may then be used with actual flowreadings to determine an amount of oil being transferred. An advantageof the piston prover is a fast proving time, requiring only a relativelysmall volume of fluid for testing.

A second type of the proving meter 502 is known as a pipe prover, inwhich, somewhat similarly to the piston prover, a ball is launched fromone end to the other of a U-shaped pipe, tripping a switch at each endof the pipe in the process. Since there is a known volume betweenswitches, the pulses from the Coriolis meter pulse output 260 arecounted between the switches, and compared between passes of the ball.The counts are then analyzed for repeatability and linearity. As aresult, a meter factor can also be determined from this procedure, whichrepresents an accuracy and/or repeatability measure of the associatedflow meter. The pipe prover is generally capable of proving relativelylarger volumes of fluid, but takes longer to do so.

In such an environment, the zero flow rate of the flowmeter 200/300 maybe expressed as a number of barrels of oil a day by which the flowmeter200/300 may be off. That is, if the zero flow rate is expressed as fivebarrels a day, then this value may be taken into account (subtracted oradded) when determining an output of the flowmeter 200/300, and/or whenperforming the proving operation described herein. As may be seen, alarge or inaccurate value of this measure may result in a relativelylarge dollar value of oil being miscalculated.

Such miscalculations may be avoided or minimized by obtaining anaccurate, averaged value for a zero flow rate of the flowmeter 200/300,after obtaining zero flow by closing upstream and downstream valves 506.As described, the operator of the flowmeter 200/300 may simply press thebutton 245 to obtain an averaged zero flow value, which may thereafterbe used during proving and other operations of the flowmeter 200/300.

Moreover, in a case where the resulting zero value is large, or isbecoming larger over time, a determination may be made that a totalre-calibration of the flowmeter 200/300 is required, or that some otherdefect of the flowmeter 200/300 has occurred. Similarly, if avariability of the zero flow value, as indicated by the standarddeviation calculated by the zero checker 255, becomes large or begins toincrease over time, then a determination may be made that the flowmeter200/300 is in need of repair or replacement.

In such cases, a memory may be associated with an operation of the zerochecker 255, for storing previously-detected zero flow calibrationvalues. In this case, an alarm generator may be included in associationwith the zero checker 255, where the alarm generator includes logicrules for generating an alarm in response to a magnitude and/or rate ofchange of the zero flow calibration value(s).

Again, such determinations may be made more easily and more reliablywith the use of the flowmeter 200/300 than with the use of aconventional flowmeter, where a large zero flow value may seem toindicate a potential problem with the flowmeter 200/300, but which mayonly be a transient zero flow value that is not particularly indicativeof any larger problems. Similarly, as just referenced, use of the button245 and zero checker 255 may allow an easier determination of trends ofincreasing zero flow values (or standard deviation values), as opposedto conventional flowmeters, in which a relatively large zero flow valuemay be followed by a relatively small value, so that trends in zero flowvalue changes may be difficult or impossible to discern.

As described above, various factors may conspire to result in a presenceof an erroneous non-zero flow rate being output by a Coriolis flowmeter,even during a time of zero flow. Such factors may include, for example,varying densities of the fluids being processed, a presence of gas in anassociated flowtube, a mechanical configuration of the flowmeter orrelated components, or changes in operating temperatures of theflowmeter.

Further, although fluids such as oil and gas are discussed above, itshould be understood that many types of materials may be used inconjunction with the implementations described herein. For example, thezero checking techniques may be used in the context of other hydrocarbonmaterials, or of food and food-related materials, as well as cleaningmaterials. Similarly, the flowmeter and zero checking techniques may beused to measure density and/or mass flow of various gasses, includingair, natural gas, and elemental gasses such as Helium. As a result,applications for these and related techniques are far-ranging, includingfood industries, drug production, oil and gas processing, and variousother industries.

In all of these settings, the implementations described herein allow forfast, easy, and accurate determination of a current zero flow value,without requiring access to the internals of a digital transmitter orcontroller.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,although the above discussion is provided in terms of zero flow values,it should be understood that the button 245 and zero checker 255 may beused to determine an average value during any flow condition of theflowmeter 200/300. Accordingly, other implementations are within thescope of the following claims.

What is claimed:
 1. A system for calibrating a flowtube, the systemcomprising: a transmitter configured to induce motion in the flowtubecontaining fluid, the transmitter comprising: a contact input, ameasurement module configured to determine a sensed property valueindicative of a sensed property of the fluid based on the motion of theflowtube, and a zero-checker module configured to determine acalibration value based on the sensed property value over apre-determined time period during which the fluid contained in theflowtube is actually stationary; a first switch configured to activatethe zero-checker module, the switch coupled to the transmitter throughthe contact input, and; wherein the first switch is configured to closethe flowtube such that the fluid contained in the flowtube isstationary, and a second switch is configured to deactivate thezero-checker module and to open the flowtube such that the fluidcontained in the flowtube flows.
 2. The system of claim 1, furthercomprising a casing that surrounds the transmitter; and a removable lidthat encloses the transmitter in the casing, the removable lidconfigured to allow access to the first switch and the second switchwhile protecting the transmitter.
 3. The system of claim 2 wherein thesystem further comprises a display and the display is configured topresent the calibration value.
 4. The system of claim 3, wherein thedisplay is enclosed in the casing by the lid.
 5. The system of claim 1,wherein the calibration value comprises the sensed property value of thefluid while the fluid is stationary.
 6. The system of claim 5, whereinthe sensed property value is indicative of a sensed mass flow of thefluid contained in the flowtube and the sensed property value has avalue other than zero.
 7. The system of claim 1, wherein the calibrationvalue comprises a predetermined value.
 8. The system of claim 1 furthercomprising: drivers controlled by the transmitter that cause the motionof the flowtube, and sensors configured to sense the motion of theflowtube.
 9. The system of claim 1, wherein: the measurement moduledetermines the sensed property value when the fluid is flowing, and thetransmitter determines a corrected property value by determining adifference between the sensed property value when the fluid is flowingand the calibration value.
 10. The system of claim 1 wherein thetransmitter further comprises a pulse output module configured togenerate signals representative of the sensed property value.
 11. Thesystem of claim 1, wherein: the calibration value is displayed inresponse to a selection of the first switch, and the zero-checker moduledetermines the calibration value based on an average of the sensedproperty value determined over the pre-determined time period.
 12. Thesystem of claim 1, further comprising: a communications interfaceconfigured to communicate commands between a computer and thetransmitter; and wherein the contact input is configured to communicatewith the zero-checker module.